RTH - Why is EGR Vacuum Modulator wet with fuel?

[RescueU]

Engine's been running rough.

Pop codes for misfires on Cyl #6 often and find the spark plug tip often dark & wet. Still trying to figure out the cause for that one.

Noticed the engine running exceptionally rough and found the EGR code had also popped. Upon inspection, I found it was wet with apparently fuel. I dried outlet the filter as much as possible. Both the vacuum tubes to the R & P ports need to be replaced now, since both now slip right off and have no grip to the Vacuum Modulator ports.

Anyone experienced this in the past and know why this has occurred?

If the filter in the Vacuum Modulator was soaked in fuel, should I replace it? Can the filter be replaced itself, or must it be the entire VM?

 

[Pin_Head]

I'm at a loss for an explanation if that is fuel on the EGR modulator, but a compression test is often informative about why plugs look dark and wet.

 

[RescueU]

^ bump ^

No one has any insight on this? I find that difficult to believe.

 

[86tuning]

There's vacuum lines to the modulator only. So if you've got gas in there, somehow fuel is making it up the vacuum lines.

 

[Splangy]

Is the EGR valve working? Maybe unburned fuel from #6 is getting sucked into the modulator through the EGR valve if the valve diaphragm is torn.

Ok, that was a long shot, but its the best I can come up with right now.

 

[TYM4FUN]

Maybe check to see if your # 6 or #5 injectors are wet as well. Seals for the injectors or fuel rail could be leaking enough to spray full up in the general area? That's the only thing I could guess....

 

[CruiseOrlando]

Doesn't the charcoal canister feed back into the EGR system somewhere? Could there be a mis-wiring for the vacuum lines, or a faulty canister perhaps?

Just a thought. I'm not near my truck or a wiring diagram at the moment so I don't know how closely these are or are not related.

 

[turbo5s]

leaky injector on #6?

I like splangy's explanation, becaue it seems unikely the fuel would have gone from intake to vacuum modulator, I think it must be going through the egr pipe which appears to be bolted to head near number 6.. In which case you will need a new egr also.

 

[RescueU]

Is the EGR valve working? Maybe unburned fuel from #6 is getting sucked into the modulator through the EGR valve if the valve diaphragm is torn.

Ok, that was a long shot, but its the best I can come up with right now.

Hmm, very interesting question, splangy. How would I best check to see if the valve diaphragm is torn, or if the modulator is working properly? I've never dismantled any of the parts in the EGR system before.

 

[RescueU]

Maybe check to see if your # 6 or #5 injectors are wet as well. Seals for the injectors or fuel rail could be leaking enough to spray full up in the general area? That's the only thing I could guess....

If the seals were leaking, and by the "general area" you mean the engine compartment, then I'd expect the plenum area to be wet (which I've not detected at all). Plus, the EGR modulator and VTV are on the opposite side of the engine...but maybe I'm missing something.

Still, it's worth checking into. Thanks for the suggestion.

 

[RescueU]

leaky injector on #6?

I like splangy's explanation, becaue it seems unikely the fuel would have gone from intake to vacuum modulator, I think it must be going through the egr pipe which appears to be bolted to head near number 6.. In which case you will need a new egr also.

I guess that means I should also figure out why the 6th Cyl spark plug is getting coated in black residue (oil, fuel, etc) and misfiring, eh?

Still have sorted out how to access the 6th fuel injector area for inspection without removing the plenum. Which may be necessary, but therein lies the challenge when this is your daily driver with little opportunity for downtime.

 

[TYM4FUN]

If the seals were leaking, and by the "general area" you mean the engine compartment, then I'd expect the plenum area to be wet (which I've not detected at all). Plus, the EGR modulator and VTV are on the opposite side of the engine...but maybe I'm missing something.

Still, it's worth checking into. Thanks for the suggestion.

EGR modulator are right above those areas.... Not somewhere else in the engine bay. I have seen a handful if cars with bad injection systems leak and spray fuel.

 

[Splangy]

Hmm, very interesting question, splangy. How would I best check to see if the valve diaphragm is torn, or if the modulator is working properly? I've never dismantled any of the parts in the EGR system before.

While the engine is idling, hook up a section of vacuum hose to the egr valve and hook up the other end of the hose to manifold vacuum, a vacuum pump, or just suck on the other end (not recommended). The egr has a split "tee" vacuum port, so you'll need to block one side. This will actuate the egr valve if it's working, and cause the engine to stumble because of the exhaust gasses being recirculated at idle.

So, if the engine stumbles, the egr valve is good. (the rest of the EGR components may be shot, but you'll know the egr valve is good)

 

[98 SNAKE EATER]

Hmm, very interesting question, splangy. How would I best check to see if the valve diaphragm is torn, or if the modulator is working properly? I've never dismantled any of the parts in the EGR system before.

I've found that the best and easiest way to properly test the modulator is to remove it completely, cover the P,R and Q ports and gently suck/blow on the bottom port

If it holds vacuum and pressure, it's good

If it doesn't, it's bad

This method is much more straight forward and better than the FSM's testing procedure IMHO

Here's a link to my recent modulator thread....

https://forum.ih8mud.com/80-series-...since-ive-had-mil-401-egr-code-revisited.html


After replacing it with a new unit, I cracked the old one apart and sure enough the diaphragm was torn

 

[Grench]

And there can be another reason for getting flow up into/around the EGR valve, though this reason results in high temperature exhaust flowing into the EGR:
https://forum.ih8mud.com/80-series-tech/245912-near-rth-vacuum-modulator-meltdown.html
(clogged cat)

If that is fuel - check the #6 spark plug too. If it's seal has failed, it could be not sparking (good in this case) and allowing compressed fuel/air to spray by.

Be careful with it though - you don't want to burn you, it and your house down.